1. Field of the Invention
The present invention relates to an electrophoretic display device and method of fabrication thereof. More particularly, the present invention relates to an electrophoretic display device and method of fabrication in which an electrophoretic material is directly applied on a substrate formed with a thin-film transistor, thereby reducing fabrication costs and shortening fabrication time.
2. Description of the Related Art
An electrophoretic display device is an image display device that uses a phenomenon in which colloidal particles move to either one of the polarities when a pair of electrodes to which a voltage is applied is immersed into a colloidal solution. In contrast to a liquid crystal display device, an electrophoretic display (EPD) device has advantages such as wide viewing angle, high reflectivity, low power consumption, and the like, without using a backlight. Thus, an electrophoretic display device is expected to be widely used as a flexible display such as an electronic paper.
The EPD device has a structure in which an electrophoretic layer is interposed between two substrates. One of the two substrates is made of a transparent substrate and the other substrate is provided with an array substrate formed with a driving element to display images in a reflective mode in which light entering from the outside of the device is reflected.
FIG. 1 is a view illustrating an electrophoretic display device 1 of the related art. As illustrated in FIG. 1, the electrophoretic display device 1 may include a first substrate 20 and a second substrate 40, a thin-film transistor and a pixel electrode 18 formed on the first substrate 20, a common electrode 42 formed on the second substrate 40, an electrophoretic layer 60 formed between the first substrate 20 and the second substrate 40, and an adhesive layer 56 formed between the electrophoretic layer 60 and the pixel electrode 18.
The thin-film transistor may include a gate electrode 11 formed on the first substrate 20, a gate insulation layer 22 formed over the whole first substrate 20 formed with the gate electrode 11, a semiconductor layer 13 formed on the gate insulation large 22, and a source electrode 15 and a drain electrode 16 formed on the semiconductor layer 13. A passivation layer 24 is formed on the source electrode 15 and drain electrode 16 of the thin-film transistor.
The pixel electrode 18 is formed on the passivation layer 24 and applies a signal to the electrophoretic layer 60. A contact hole 28 is formed through the passivation layer 24, so that the pixel electrode 18 is connected to the drain electrode 16 of the thin-film transistor through the contact hole 28.
Furthermore, a color filter layer 44 and a common electrode 42 are formed on the second substrate 40. The electrophoretic layer 60 is formed on the color filter layer 44 and the adhesive layer 56 is formed on the electrophoretic layer 60. The electrophoretic layer 60 may include a capsule 70 filled with white particles 74 and black particles 76 therein. If a signal is applied to the pixel electrode 18, then an electric field is generated between the common electrode 42 and the pixel electrode 18, and the white particles 74 and the black particles 76 inside the capsule 70 are moved in a direction of the common electrode 42 or pixel electrode 18 by the electric field, thereby displaying an image.
For example, when a negative (−) voltage is applied to the pixel electrode 18 on the first substrate 20 and a positive (+) voltage is applied to the common electrode 42 on the second substrate 40, white particles 74 with positive (+) charge are moved to the side of the first substrate 20 and black particles 76 with negative (−) charge are moved to the side of the second substrate 40. In this state, if light is entered from the outside, i.e., an upper portion of the second substrate 40, then incident light is reflected by the black particles 76, thereby implementing black on the electrophoretic display device.
In contrast, when a positive (+) voltage is applied to the pixel electrode 18 on the first substrate 20 and a negative (−) voltage is applied to the common electrode 42 on the second substrate 40, white particles 74 with positive (+) charge are moved to the side of the second substrate 40 and black particles 76 with negative (−) charge are moved to the side of the first substrate 20. In this state, if light is entered from the outside, i.e., an upper portion of the second substrate 40, then incident light is reflected by the white particles 74, thereby implementing white on the electrophoretic display device.
An electrophoretic display device having the foregoing structure illustrated in FIG. 1 may have the following problems.
First, the method of fabricating an electrophoretic display device in the related art has difficulty in attaching the first substrate and the second substrate.
In the electrophoretic display device of the related art, the first substrate 20 and second substrate 40 are individually fabricated, and then the first substrate 20 and second substrate 40 are attached to each other using an adhesive layer 56 to complete the process. More specifically, a thin-film transistor for driving a unit pixel and the pixel electrode 18 for applying an electric field to the electrophoretic layer are formed on the first substrate 20, and the common electrode 42, the color filter layer 44, the electrophoretic layer 60 and the adhesive layer 56 are formed on the second substrate 40. Then, the first substrate 20 and the second substrate 40 are attached to each other to complete the process.
However, the unit pixel in a typical electrophoretic display device may be formed with a small size of less than 150 micrometer in the height and width thereof Thus, it may be difficult to accurately align the electrophoretic layer. If the electrophoretic layer is not accurately aligned with the first substrate formed with a thin-film transistor when aligning the electrophoretic layer, then an electric field is not accurately delivered to electrophoretic particles, thereby causing a driving error.
Second, the method of fabricating an electrophoretic display device in the related art has a complicated fabrication process.
The first substrate 20 and the second substrate 40 are fabricated in a different process, and then transferred by a transfer means and attached to each other in the attachment process, and thus it may be impossible to form an in-line fabrication process.
Third, electrostatic discharge generated during the process of attaching the first substrate and second substrate may cause failure in the initial alignment of electrophoretic particles.
The common electrode 42, the color filter layer 44 and the electrophoretic layer 60 are formed on the second substrate 40, and the adhesive layer 56 is coated on the electrophoretic layer 60. Furthermore, a protection film is adhered to the adhesive layer 56 in order to prevent the reduction of the adhesive force of the adhesive layer 56 and prohibit foreign materials from being adhered to the adhesive layer 56. However, the protection film should be peeled off from the second substrate 40 to adhere the second substrate 40 to the first substrate 20. Electrostatic charge is generated during the process of peeling off the protection film and may cause misalignment in the initial alignment of electrophoretic particles. The misalignment of electrophoretic particles due to electrostatic discharge may generate moiré with a comb-tooth-shaped pattern during the operation of the electrophoretic display device.